Fabrication of high-speed single photon detectors in NbN for quantum information processing

International audienceAbstract. We describe the collective fabrication and characterization of superconducting single photon detectors (SSPD) made of a superconducting NbN meander, suitable for near-infrared applications. The NbN layer acting as the photon absorber is deposited epitaxially on a three inch diameter R-plane Sapphire heated substrate by DC-Magnetron sputtering from a Nb target in a reactive mixture of nitrogen and argon gas. Very thin NbN (~4 nm) films superconducting up to 12 K with a rather large critical current density are in-situ covered by a 1.4 nm thick room temperature sputtered AlN layer protecting NbN from oxidation. Two reliable patterning processes has been developed successfully, one based on electron beam lithography, the second based on selective NbN film anodization under an AFM tip. The filling factor obtained with 150 nm wide stripes in the meander pixel is about 0.5 with e-beam lithography and improved up to 0.8 with AFM patterning. In order to achieve an improved optical coupling of the SSPD by using wafers integrating ion implanted IR waveguides, growth studies of NbN layers have been focused on R-plane Sapphire and silicon substrates. We present optical and superconducting properties of NbN layers by FTIR, ellipsometry and STM